Compatibility of the Vinylidene Ligand and Perfluorophenoxide

This study demonstrates the stability of the Ru-vinylidene moiety toward installation of a perfluorophenoxide ligand. The room-temperature reaction of RuCl(dcypb)(μ-Cl)₃Ru(dcypb)(N₂) (3) with TlOC₆F₅ and excess tert-butylacetylene yields mononuclear Ru(OC₆F₅)₂(dcypb)(CCHBu^t) (6, dcypb = 1,4-bis(dicyclohexylphosphino)butane). Intermediates en route to 6 are the face-bridged dimers RuCl(dcypb)(μ-Cl)₃Ru(dcypb)(CCHBu^t) (4a) and [{Ru(dcypb)(CCHBu^t)}₂(μ-Cl)₃]OC₆F₅ (5·OC₆F₅):  the cation in the latter was characterized as its PF₆ salt (reaction halting at 5·PF₆ on use of TlPF₆ in place of TlOC₆F₅). Edge-bridged, dicationic [{RuCl(dcypb)(CCHBu^t)}₂(μ-Cl)₂](OC₆F₅)₂ (8) is also a probable intermediate in this reaction pathway:  although not observed directly, the dication was isolated in low yields as its BAr^f₄ salt, on reaction of 5·PF₆ with NaBAr^f₄ (BAr^f₄^- = [B{C₆H₃(CF₃)₂-3,5}₄]^-). A minor byproduct in the synthesis of 6 is acetylide Tl[{Ru(C⋮CBu^t)(dcypb)}₂(μ-Cl)₃] (7), formed by deprotonation of the vinylidene ligand in 5·OC₆F₅ by TlOC₆F₅. (An alternative representation of 7 as a covalent Ru(μ-Cl)₂Tl species is supported by X-ray evidence, at least in the solid state.) Importantly, the deprotonation reaction is reversible, and competing reprotonation of 7 by the phenol coproduct enables re-formation of 5·OC₆F₅. Nucleophilic attack by the aryloxide anion on the metal center enables complete and irreversible transformation to 6, illustrating the mutual compatibility of the vinylidene and perfluorophenoxide ligands. As expected from the high thermodynamic stability of the Ru₂(μ-Cl)₃ entity, complexes 5·PF₆ and 5·Cl exhibit low activity in ring-opening metathesis polymerization of norbornene. Mononuclear 6, containing four nonlabile ligands cis to the vinylidene moiety, is likewise quite unreactive until activated by protonolysis of aryloxide. Product identities were established by ¹H, ¹³C, and ³¹P NMR and IR spectroscopy, and (6, 7, 8) X-ray crystallography.